METHOD AND DEVICE FOR DETERMINING THE DIRECTION TO A FAULT ON A POWER TRANSMISSION LINE

Abstract: A method and a device for determining the direction to a fault on a power transmission line in relation to a measuring station with the aid of phase currents and voltages, measured in the measuring station, by means of which change values DELTA U in the phase voltage, change values in the phase voltage DELTA UM of a line model and change values in the derivative DELTA I' of the phase current can be determined, and wherein for each measuring loop phase-ground the signal DELTA QL = ( DELTA U- DELTA UM). DELTA UI' is formed and if this value is smaller than a negative value assumed in advance, a fault lying ahead, in relation to the measuring station, has been detected, and wherein for each measuring loop phase-ground the signal DELTA QB = DELTA U. DELTA UI' is formed and if this value is greater than a positive value assumed in advance, a fault lying behind, in relation to the measuring station, has been detected.

Description: Method and device for determining the direction to a fault on a power transmission line TECHNICAL FIELD It is important to protect components included ih power or transmission networks, such as power lines, busbars, trans¬ formers, etc. The present invention relates to a method and a device for protection which indicates in which direction, in relation to two or more measuring points, a fault has occurred, a so-called directional detecting protection. In this connection the term "zone of supervision" of a protec¬ tion device is used, and an internal fault is defined as a fault which lies within the zone of supervision of the protection device. A fault which lies outside the zone of supervision and which can be detected is consequently called an external fault. Starting from a measuring point, direc¬ tional detection can also be obtained, and in that connec¬ tion the term "a fault lying ahead" is used when referring to a fault occurring in the direction of supervision of the protection device, and the term "a fault lying behind" is used when referring to a fault occurring in the opposite direction. BACKGROUND ART When a fault occurs in a power transmission network, travelling waves arise which move along the line. It is known to use the direction of movement of these travelling waves as a measuring point to determine the direction to the location of the fault. US patent No. 3 878 460 discloses how to utilize the fact that in those travelling waves, which from a fault point move in towards the measuring point of the protection device, the current and voltage waves have different signs. If the voltage is designated "u", the current "i", and the wave impedance ZQ, the equation u = -ZQ-i is obtained in the case of a fault lying ahead. If the fault is located behind the measuring point, the current and voltage waves have the same signs, whereby the equation u = Zn-i is obtained for a external fault lying behind. To obtain a measure of the travelling waves, the fundamental frequency parts of the current and voltage signals are here filtered away. A directional wave detector according to US 4 351 Oil (= SE 7803868-4) is using an alternative in which, instead of treating the voltage and current waves separately, the product of voltage and current is formed, that is, the power or its integral, that is, the energy. The direction to a fault can then be determined by the sign of the instan¬ taneous power or energy change. For an internal fault or a fault lying ahead, a negative sign of the power or energy change is then obtained, and, in a corresponding way, a positive sign is obtained for an external fault or a fault lying behind. Another way of obtaining directional detection of faults on a power line located between two stations P and Q is clear from US 4 731 689. The method is based on the fact that with access to data for a faultless power line, a wave guide model of the power line can be determined. With the aid of the wave model and measured currents and voltages in the stations, the voltage distribution along the power line can be calculated. The direction to a fault is determined by studying locally in a station changes in calculated voltages in the two stations. If a fault occurs between the stations, the voltage change in station Q between the voltage prior to the fault and after the fault may be calculated, with the wave model, to be IΔUql and the corresponding voltage change in station P may be calculated to be IΔUpl, and if IΔUql - IΔU l > 0 this means that there is a fault on the line side of station P, that is, a fault lying ahead. To be able to carry out the directional determination accor¬ ding to the invention, access is also needed to the corre- sponding change values or Δ-values for both voltage and current. Several alternative methods are available for obtaining these values. One such method is described in the above-mentioned US 4 731 689 in the following way: Δ-values "... are obtained by adding the (voltage) values of two consecutive half-periods" . Another alternative is to take the difference between the value in question and a value one period earlier. The generation of these Δ-values will take placed, according to the description, in a so-called Δ- filter. In addition, it is necessary to have access to some model of the line which describes its properties. Also in this case there are several more or less complete , models which take the line data into account. One such model may, for example, be: UM = R-I+L-I'+Rn-In+Ln-In' Here, UM designates a model phase voltage, R designates the resistance of the line, I is the phase current, L is the inductance of the line, I' is the derivative of the phase current, Rn is the resistance of the ground loop, In is the ground current, Ln is the inductance of the ground loop, and In' is the derivative of the ground current. The formation of the phase voltages of the line model will be carried out, according to the following description, in a so-called "Line model" . SUMMARY OF THE INVENTION, ADVANTAGES The principle of determining the direction to a fault on a power transmission line according to the invention will be described partly for directional determination in case of a fault in one phase and partly for directional determination in case of a phase-to-phase fault. The condition is that access is had to the phase voltage U, the phase current I, the derivative I' of the phase current and, via a line model, the model voltage UM, and that change values can be determined, via a Δ-filter, for these quanti¬ ties, that is, ΔU, ΔUM and ΔI ' for each measuring loop R- ground, S-ground, T-ground, R-S, S-T, and T-R. By forming the difference ΔU - ΔUM for each measuring loop phase-ground and multiplying this difference by ΔI ' , a signal ΔQL is obtained. If the value of this signal, when a fault has been detected, is smaller than a negative value assumed in advance, this means that there is a fault "L" lying ahead, in relation to the measuring station, on the line and that, together with the other criteria for tripp¬ ing, the phase or phases in question may be disconnected. By multiplying ΔU by ΔI ' for each measuring loop, a signal ΔQB is obtained. If the value of this signal, when a fault has been detecteded, is greater than a positive value assumed in advance, this means that there is a fault "B" lying behind, in relation to the measuring station, on the line and that disconnection of the phase or phases in question can be blocked. For a phase-to-phase fault, the differences between the Δ- values for the different phase-ground measuring loops can be formed, and, in the same way as above, ΔQL-values and ΔQB- values may be obtained for the phase-to-phase faults described above. A more detailed explanation of the method will become clear from the following description of embodiments. The method for directional determination according to US patent 4 351 011 mentioned above is based on the sign of the instantaneous power change, that is Δl-ΔU. Because the impe¬ dances in a power network are preferably inductive, the relationship between the current and voltage changes in the event of a fault will be determined by this fact. A more detailed study of the polarity of the current and voltage changes under these conditions shows that they have diffe¬ rent signs during the first few milliseconds after the occurrence of a fault. Thereafter, however, the current and voltage changes will have the same polarity. Admittedly, this method provides the correct direction to the fault during the first few milliseconds, but because after this time they have the same polarity, problems may arise. Further studies have shown that a distinct and unambiguous negative sign of the product ΔI'-ΔU is obtained since the polarities of these two factors remain different after the occurrence of a fault. The advantage of using this criterion for directional determination etc. is thus that the descri- bed uncertainty of prior art methods has been eliminated. DESCRIPTION OF THE PREFERRED EMBODIMENTS A complete embodiment of the method according to the inven- tion for the three phases of a power transmission network will described with reference to the accompanying figure. According to the invention, Δ-values ΔU, ΔUM and ΔI ' are formed for each measuring loop according to the above, that is ΔUR, ΔUMR, ΔI 'R and ΔUS, ΔUMS, Δl'S and ΔUT, ΔUMT, Δl'T on the basis of phase voltages and currents UR, IR, US, IS, UT and IT via low-pass filters IR, IS and IT, current diffe¬ rentiators 2R, 2S and 2T, line models 3R, 3S and 3T and Δ- filters 4R, 4S and 4T. It should be pointed out here that the figure, in order to become more clear, is somewhat sim¬ plified as regards the line models. As will be clear from the above-described line model, the ground current In and its derivative In' are included. These quantities are formed in the simplest way by summing the phase currents and the derivatives of the phase currents, respectively. Therefore, in a complete diagram there are connections between the three line models, which is indicated in the figure by the dashed lines between the line models. Otherwise, it is assumed here that the line models are provided with the current network data according to the description under the "Background Art" above. In accordance with the description of the invention, ΔQLR, ΔQBR, ΔQLS, ΔQBS, ΔQLT and ΔQBT are formed with the aid of the summators 5R, 5S and 5T, the multipliers 6R, 6S and 6T and the multipliers 7R, 7S and 7T as ΔQLR = (ΔUR - ΔUMR) -ΔI'R ΔQBR = ΔUR-ΔI'R ΔQLS = (ΔUS - ΔUMS)-ΔI'S ΔQBS = ΔUS-ΔI'S ΔQLT = (ΔUT - ΔUMT) -Δl'T ΔQBT = ΔUT-Δl'T In the comparators 8R, 8S and 8T the respective ΔQL-values are then compared with a negative constant "a" assumed in advance, and if one or more of the ΔQL-values after a fault has been detected is/are smaller than "a", a logical "1" is obtained, designated LR, LS and LT, respectively. The significance of these signals is that there is a fault lying ahead in one phase, in several phases, or in all phases. In parallel therewith, the respective ΔQB-values are com¬ pared in the comparators 9R, 9S and 9T with a positive constant "b" assumed in advance, and if one or more of the ΔQB-values after a fault has been detected is/are greater than "b", a logical "1" is obtained, designated BR, BS and BT, respectively. The significance of these signals is that there is a fault lying behind in one phase, in several phases, or in all the phases and that disconnection of the faulty phase or phases can be blocked by means of the signals . The most frequent fault in a power network is a single-phase ground fault. In certain safety engineering applications, however, it is desirable to obtain information whether there is a fault in only one of the phases and in which phase the fault has occurred. When multi-phase faults occur, it is also desirable to be able to identify which phases are involved. The embodiment described above for information about faults lying ahead and faults lying behind can also be used to satisfy these purposes. This can be done with the aid of the Δ-values described. For this purpose, the Δ- signals for the phase-to-phase measuring loops according to the above are needed, that is, ΔURS corresponding to the difference between ΔUR and ΔUS, and in similar manner the differences ΔUMRS, ΔI'RS, ΔUST, ΔUMST, Δl'ST, ΔUTR, ΔUMTR and Δl'TR. These signals are formed with the aid of the summators 10RS, 11RS, 12RS, 10ST, 11ST, 12ST, 10TR, 11TR and 12TR. In similar manner as described above, ΔQLRS, ΔQBRS, ΔQLST, ΔQBST, ΔQLTR and ΔQBTR are formed with the aid of the summa¬ tors 13RS, 13ST and 13TR, the multipliers 14RS, 14ST and 14TR, and the multipliers 15RS, 15ST and 15TR as ΔQLRS = ((ΔUR -ΔUS) - (ΔUMR -ΔUMS) ) • (ΔI 'R - ΔI'S) ΔQBRS = (ΔUR -ΔUS)- (Δl'R - ΔI'S) ΔQLST = ((ΔUS -ΔUT) - (ΔUMS - ΔUMT)) - (Δl'S - Δl'T) ΔQBST = {ΔUS - ΔUT)- (ΔI'S - Δl'T) ΔQLTR = ((ΔUT -ΔUR) - (ΔUMT - ΔUMR)) - (Δl'T - ΔI'R) ΔQBTR = (ΔUT - ΔUR) - (Δl'T - ΔI'R) In the comparators 16RS, 16ST and 16TR, the ΔQL-values are then compared with a negative constant "c" assumed in ad¬ vance, and if one or more of the ΔQL-values after a fault has been detected is/are smaller than "c", a logical "1" is obtained, designated LRS LST and LTR. In parallel therewith, the respective ΔQB-values are compa¬ red in the comparators 17RS, 17ST and 17TR with a positive constant "d" assumed in advance, and if one or more of the ΔQB-values after a fault has been detected is/are greater than "d", a logical "1" is obtained, designated BRS, BST and BTR, respectively. With the signals obtained in the above manner, it is possible, via a Boolean arrangement, for example as is clear from the figure with the "AND" elements 18L, .18B and 18R, 19L, 19B and 19S, 20L, 20B and 20T, to form the signals R = LR-LRS-LTR- (BR-BRS-BTR) LS- LST-LRS- (BS-BST-BRS) T = LT-LTR-LST- (BT-BTR-BST) To ensure the formation of the above signals, it may be suitable to introduce the time-lag elements 21R and 21B, 22S and 22B, 23T and 23B as will be clear from the figure. Now, thus, the necessary signals are available for identi¬ fying single-phase faults to ground, lying ahead, for all phases as well as for identifying multi-phase faults. A suitable method therefor can also be executed with a Boolean arrangement with "AND" elements 24, 25 and 26 executing the Boolean expressions RU = R-IT- ' T " SU = S-~R~-T~ TU = T-~RMT The signal RU thus indicates that a fault which has occurred is a single-phase fault to ground, lying ahead, in the R- phase, SU correspondingly indicates a single-phase fault to ground I, lying ahead, in the S-phase and TU correspondingly indicates a fault lying ahead in the T-phase. The indication of multi-phase faults may be derived with the aid of the "AND" elements 27, 28 and 29 executing the Boolean expressions: RSU = R-S STU = S-T TRU = T-R where the signal RSU indicates only a fault lying ahead in the phases R and S, the signal STU only a fault lying ahead in the phases S and T, and the signal TRU only a fault lying ahead in the phases T and R. In a corresponding manner, information as to the occurrence of a fault lying behind in any individual phase may be obtained. Such a signal BRU for the R-phase is directly available in the figure as the signal after the time-lag element 21B, that is, BRU = BR-BRS-BTR which means that the phase R has a fault laying behind. The corresponding signal BSU for the S-phase is directly avail¬ able in the figure as the signal 22B, that is, BSU = BS-BST-BRS which means that the phase S has a fault lying behind. The corresponding signal BTU for the 3-phase is directly available in the figure as the signal after the time-lag element 22B, that is, BTU = BT-BTR-BST which means that the phase T has a fault lying behind. As an example of a logic circuit, it can be seen that, in the case of a single-phase fault R to ground, only the signals LR, LRS and LTR will consist of "1" (ones) whereas all the other signals or at least LST are "0" (zero) . This means that the signal R becomes "1" (one) whereas the signals S and T become "0" (zeros) . This then means that only the signal RU becomes a "1" (one) indicating a ground fault in the R-phase lying ahead. In case of a two-phase fault R-S the signals LR, LRS, LTR, LS and LST will consist of "1" (ones) whereas in most cases all other signals are "0" (zeros) . This means that the signals R and S become "1" (ones) whereas T becomes "0" (zero) which in turn means that all RU, SU, TU and STU as well as TRU become "0" (zeros) whereas RSU becomes a "1" (one) that is, a fault lying ahead in the R- and S-phases. In a complete line protection system, there are three diffe¬ rent functions which are influenced by the signals produced above, namely, for the directional comparison, for the selection of measuring loop, and for phase selection for tripping circuit breakers. The numerical values of the constants a, b, c and d are determined partly on the basis of the ratings of the current and voltage transformers which are used, partly depending on how sensitive the protection device is to be, and partly depending on whether it is a power network with considerable harmonics. If, for example, the secondary data of the used current transformers are 110 volts and 1 ampere, then "a" should lie within the range 0.5 - 12; preferably a = 6.5 "b" should lie within the range 0.25 - 5; preferably b = 2.5 "c" should lie within the range 1 - 22; preferably c = 11 "d" should lie within the range 0.5 - 10; preferably d = 4.5. The scope of the invention comprises different embodiments which may consist of separate units as described above, or more or less integrated, possibly program-controlled embodiments.

Claims: CLAIMS 1. A method for determining the direction to a fault on a power transmission line in relation to a measuring station starting from the phase currents IR, IS, IT and the phase voltages UR, US, UT of the power transmission line, measured in the measuring station, and with access to differentiating units for forming the derivatives I' of the phase currents, units for forming a model voltage UM of the power line on the basis of a line model, (Δ-)units for determining changes in measured and calculated quantities as well as summing and multiplying units, said method being characterized in that for each measuring loop R-ground, S-ground, T-ground, R-S, S-T and T-R, the change values ΔU, ΔUM and ΔI ' are formed, that the difference ΔU - ΔUM is formed and multiplied by ΔI' whereby a signal ΔQL is obtained and that ΔU is multiplied by Δl ' whereby a signal ΔQB is obtained, and that when a fault has been detected ΔQL is compared with an assumed negative value, and that if ΔQL is smaller that said value, a fault "L" lying ahead, in relation to the measuring station, has been detected on the power line, whereby measures can be taken to disconnect the faulty phase or phases, and that ΔQB is compared with an assumed positive value and if ΔQB is greater than said value, a fault "B" lying behind, in relation to the measuring station, has been detected on the power line, whereby disconnection of the faulty phase or phases can be blocked. 2. A method for determining the direction to a fault on a power transmission line according to claim 1, wherein the model voltage UM per phase is formed with the aid of a line model UM = R-I + L-I' + Rn-In + Ln-In' wherein R denotes the resistance of the line, I is the phase current, L is the inductance of the line, I' is the deriva¬ tive of the phase current, Rn is the resistance of the ground loop, In is the ground current, In' is the derivative of the ground current, and Ln is the inductance of the ground loop. 3. A device for carrying out the method according to claim 1 for determining the direction to a fault on a power trans¬ mission line in relation to a measuring station, wherein on the basis of the phase currents IR, IS, IT and the phase voltages UR, US, UT of the power transmission line, via low- pass filters (IR, IS, IT) , current differentiators (2R, 2S, 2T) for determining the derivative I' of the phase currents, line models (3R, 3S, 3T) for determining a model voltage UM for each phase and Δ-filters (4R, 4S, 4T) , the change values ΔUR, ΔUMR, ΔI'R, ΔUS, ΔUMS, Δl 'S and ΔUT, ΔUMT, Δl'T are determined, the device being characterized in that with a first summator (5R) and a first multiplier (6R) , the following signal is formed ΔQLR = (ΔUR - ΔUMR) -ΔI'R, and that in a first comparator (8R) said signal is compared with a negative constant "a" and if the signal is smaller than the constant "a" a logical "1"-signal LR is obtained for tripping the R-phase because of a fault lying ahead in the R-phase, and that with a second summator (5S) and a second multiplier (6S) , the following signal is formed ΔQLS = (ΔUS - ΔUMS)-ΔI'S, and that in a second comparator (8S) said signal is compared with the negative constant "a" and if the signal is smaller than the constant "a", a logical "l"-signal LS is obtained for tripping the S-phase because of a fault lying ahead in the S-phase, that with a third summator (5T) and a third multiplier (6T) , the following signal is formed ΔQLT = (ΔUT - ΔUMT) -Δl'T, and that in a third comparator (8T) said signal is compared with the negative constant "a" and if the signal is smaller than the constant "a", a logical "l"-signal LT is obtained for tripping the T-phase because of a fault lying ahead in the T-phase , and that with a fourth multiplier (7R) , the following signal is obtained ΔQBR = ΔUR-ΔI'R, and that in a fourth comparator (9R) said signal is compared with a positive constant "b" and if the signal is greater than the constant "b", a logical "1"-signal BR is obtained for blocking the R-phase because of a fault lying behind in the R-phase, and that with a fifth multiplier (7S) , the following signal is obtained ΔQBS = ΔUS-ΔI'S, and that with a fifth comparator (9S) said signal is compared with the positive constant "b" and if the signal is greater than the constant "b", a logical "1"-signal BS is obtained for blocking the S-phase because of a fault lying behind in the S-phase, and that with a sixth multiplier (7T) the following signal is obtained ΔQBT = ΔUT-Δl'T, and that with a sixth comparator (9T) said signal is compared with the positive constant "b" and if the signal is greater than the constant "b", a logical "l"-signal BT is obtained for blocking the T-phase because of a fault lying behind in the R-phase, and wherein the numerical value of the constant "a" lies within the interval 0.5 - 12, and wherein the numerical value of the constant "b" lies within the interval 0.25 - 5, and that with a fourth, a fifth, a sixth and a seventh summator (10RS, 11RS, 12RS, 13RS) and a seventh multiplier (14RS) the following signal is obtained ΔQLRS = ((ΔUR - ΔUS) - (ΔUMR - ΔUMS))- (ΔI'R - ΔI'S), and that in a seventh comparator (16RS) said signal is compared with a negative constant "c" and if the signal is smaller than the constant "c", a logical "1"-signal LRS is obtained for tripping the R- and S-phases because of a fault lying ahead in the R- and S-phases, and that with an eighth, a ninth, a tenth and an eleventh summator (10ST, 11ST, 12ST, 13ST) and an eighth multiplier (14ST) the following signal is obtained ΔQLST = ((ΔUS - ΔUT) - (ΔUMS - ΔUMT)) - (ΔI'S - Δl'T), and that in an eighth comparator (16ST) said signal is compared with the negative constant "c" and if the signal is smaller than the constant "c", a logical "1"-signal LST is obtained for tripping the S-and T-phases because of a fault lying ahead in the S- and T-phases, and that with a twelfth, a thirteenth, a fourteenth and a fifteenth summator QOTR ' , 11TR, 12TR, 13TR) and a ninth multiplier (14TR) the following signal is obtained ΔQLTR = ((ΔUT - ΔUR) - (ΔUMT - ΔUMR) ) - (Δl'T - Δl'R), and that in a ninth comparator (16TR) said signal is compared with the negative constant "c" and if the signal is smaller than the constant "c", a logical "1"-signal LTR is obtained for tripping the T- and R-phases because of a fault lying ahead in the T- and R-phases, and that with the fifth and sixth summators (11RS, 12RS) and a tenth multiplier (15RS) the following signal is obtained ΔQBRS = (ΔUR - ΔUS)- (ΔI'R - ΔI'S) , and that in a tenth comparator (17RS) said signal is compared with a positive constant "d" and if the signal is greater than the constant "d", a logical "l"-signal BRS is obtained for blocking the R- and S-phases because of a fault lying behind in the R- and S-phases, and that with the ninth and tenth summators (11ST, 12ST) and an eleventh multiplier (15ST) the following signal is obtained ΔQBST = (ΔUS - ΔUT) . {ΔI'S - Δl'T), and that in an eleventh comparator (17ST) said signal is compared with the positive constant "d" and if the signal is greater than the constant "d", a logical "l"-signal BST is obtained for blocking the S- and T-phases because of a fault lying behind in the S- and T-phases, and that with the ninth and tenth summators (11ST, 12ST) and a twelfth multiplier (15TR) the following signal is obtained ΔQBTR =(ΔUT - ΔUR)- (Δl'T - ΔI'R), and that in a twelfth comparator (17TR) said signal is compared with the positive constant "d" and if the signal is greater than the constant "d" a logical "1"-signal BTR is obtained for blocking the T- and R-phases because of a fault lying behind in the T- and R-phases, and wherein the numerical value of the constant "c" lies within the interval 1 - 22, and wherein the numerical value of the constant "d" lies within the interval 0.5 - 10. 4. A device according to claim 3 for determining the direc¬ tion to a fault on a power transmission line in relation to a measuring station, and for determining whether there is a fault on a phase, and for determining this phase, and for determining whether there is a fault on two phases, and for determining these two phases with the aid of the logical signals LR, LS, LT, BR, BS, BT, LRS, LST, LTR, BRS, BBST and BTR, characterized in that with a first, a second, and a third "AND" element (18L, 18B, 18R) the following logical signal is formed R = LR-LRS-LTR- (BR-BRS-BTR) and that with a fourth, a fifth, and a sixth "AND" element (19L, 19B, 19R) the following logical signal is formed S = LS- LST-LRS- (BS-BST-BRS) and that with a seventh, an eight, and a ninth "AND" element (20L, 20B, 20R) the following logical signal is formed T = LT-LTR-LST- (BT-BTR-BST) and that with a tenth "AND" element (24) the following logical signal is formed RU = R- ' S-T which indicates that a fault lying ahead has occurred in the R-phase, and that with an eleventh "AND" element (25) the following logical signal is formed SU = S-R- " T which indicates that a fault lying ahead has occurred in the S-phase, and that with a twelfth "AND" element (26) the following logical signal is formed TU = T-R " - " S~ which indicates that a fault lying ahead has occurred in the T-phase, and that with a thirteenth "AND" element (27) the following logical signal is formed RSU = R-S which indicates that a fault lying ahead has occurred in the R- and S-phases, and that with a fourteenth "AND" element (28) the following logical signal is formed STU = S-T which indicates that a fault lying ahead has occurred in the S- and T-phases and that with a fifteenth "AND" element (29) the following logical signal is formed TRU = T - R which indicates that a fault lying ahead has occurred in the T- and R-phases, and that the second "AND" element (18B) forms the following logical signal BRU = BR-BRS-BTR which indicates that a fault lying behind has occurred in the R-phase, and that the fifth "AND" element (19B) .forms the following logical signal BSU = BS-BST-BRS which indicates that a fault lying behind has occurred in the S-phase, and that the eighth "AND" element (20B) forms the following logical signal BTU = BT-BTR-BST which indicates that a fault lying behind has occurred in the T-phase.

Inventors: NIMMERSJOE GUNNAR, NIMMERSJOE, GUNNAR
Applicants: ASEA BROWN BOVERI, ASEA BROWN BOVERI AB
Application year: 1994
Main classification: H02H7
IPC codes: H02H7